12 research outputs found

    Investigations of Pressurized Lu–N–H Materials by Using the Hybrid Functional

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    Recently, Lu–N–H materials were reported to have room-temperature superconductivity, the Hubbard U correction on Lu’s f-electrons is necessary, and a constant U = 5.5 eV was applied to different Lu–N–H configurations. The following simulations demonstrate that different U values lead to different superconducting transition temperatures. Here, the structural and electronic Lu–N–H properties at high pressure (0–10 GPa) are systematically investigated based on the hybrid functional. We show that different Lu–N–H configurations should possess different U values varying from 6.4 to 7.4 eV. Furthermore, at pressures ranging from 0 to 1 GPa, the f and d band centers of N-doped LuH3 show oscillation or even plateau, and the band gap of insulators also shows a platform, consistent with the pressure range for room-temperature superconductivity in Lu–N–H. Our work provides insight into understanding Lu–N–H materials and other hydrogen-rich superconductors based on rare-earth elements

    NMR Chemical Shifts of <sup>15</sup>N‑Bearing Graphene

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    The <sup>15</sup>N NMR chemical shifts of possible nitrogen-containing moieties at edges and defects of graphene are investigated by using the first-principles method. Our computational results show that pyridine-like and graphite-like N can be rather easily identified using the <sup>15</sup>N NMR technique, in agreement with experiment. On the other hand, pyridinium-like <sup>15</sup>N is hardly distinguished from the pyrrole-like one using the NMR, because these <sup>15</sup>N nuclei give nearly overlapping signals. However, our simulations suggest that <sup>1</sup>H NMR is useful to discriminate between them; the NMR chemical shifts of <sup>1</sup>H directly bonded with pyridinium-like and pyrrole-like N along the armchair edge are estimated to be 0.8 and 10.1 ppm, respectively, while the corresponding chemical shift for pyridinium-like N along the zigzag edge is located between them. The <sup>15</sup>N NMR signals for various moieties at edges we considered are found to be similar to the corresponding ones at defects except for pyridine-like nitrogens. Conversely, the <sup>15</sup>N NMR chemical shifts are altered sensitively by the degree of aggregation of pyridine-like <sup>15</sup>N atoms both along armchair edges and at defect sites. Interestingly, the graphite-like <sup>15</sup>N doped along zigzag edges, which was attributed in our previous work to an active configuration for oxygen reduction reaction at the cathode of fuel cells, is identifiable via NMR irrespective of the details of samples such as edge terminations, dopant distributions, and graphene sizes

    G-T nucleotide distribution on 1st codon position of all four sets of ORFs.

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    <p>(a) G-T distribution of 4835 positive and 3515 negative samples in training sets. (b) G-T distribution for 1256 predicted genes and 488 rejected spurious ORFs and all 1744 ORFs are those originally labeled as dubious or uncharacterized by the SGD annotation.</p

    List of misclassified genes in 10-fold cross-validation.<sup>*</sup>

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    *<p>All the 15 misclassified ORFs (with an average length of 296.6 nucleotides) are small ORFs, which are usually difficult to identify.</p

    Performance for all the 63 groups of measurements in cross-validation.<sup>*</sup>

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    *<p>Six measurements are represented as following: 1/mono-nucleotide frequencies, 2/di-nucleotide frequencies, 3/mono-codon composition, 4/di-codon composition, 5/mono-amino acid usages, 6/di-amino acid usages.</p>a<p>The boldface letter indicates the group with highest accuracy among the 63 combinations.</p

    Interaction Mechanism of Re(VII) with Zirconium Dioxide Nanoparticles Archored onto Reduced Graphene Oxides

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    Zirconium oxide archored onto reduced graphene oxides (ZrO<sub>2</sub>@rGO) was fabricated via a hydrothermal method and used for Re­(VII) removal from aqueous solutions. Scanning electron microscopy, Fourier transferred infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy were used to characterize the as-prepared ZrO<sub>2</sub>@rGO. The results indicated that ZrO<sub>2</sub> was successfully decorated on rGO. The maximum sorption capacity of ZrO<sub>2</sub>@rGO toward Re­(VII) was 43.55 mg/g. ZrO<sub>2</sub>@rGO exhibited enhanced sorption capacity for Re­(VII) in comparison with bare ZrO<sub>2</sub> or rGO. The sorption kinetics could be described by the pseudo-second-order equation. The sorption process of Re­(VII) on ZrO<sub>2</sub>@rGO was endothermic and spontaneous. X-ray photoelectron spectroscopy indicated the formation of an ionic bond of Zr–O with Re­(VII). According to the density functional theory calculations, O<sub>Re</sub>–Zr bonds on the surface of the monoclinic ZrO<sub>2</sub> plane (m-ZrO<sub>2</sub>) (111) plane and tetragonal ZrO<sub>2</sub> (t-ZrO<sub>2</sub>) (111) plane were formed when Re­(VII) sorbs. The sorption energy of Re­(VII) onto the t-ZrO<sub>2</sub> (111) plane was 3.87 eV, being higher than that of Re­(VII) onto m-ZrO<sub>2</sub> (1.26 eV)

    High-Pressure Synthesis of CeOCl Crystals and Investigation of Their Photoluminescence and Compressibility Properties

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    The well-crystallized mixed anions compound cerium oxychloride (CeOCl) was successfully synthesized by a high-pressure solid-state metathesis reaction. The photoluminescence experiment shows that the CeOCl, with a band gap of ∼3.05 eV, has good violet-blue emission properties. And first-principles calculations of the band structures show that CeOCl is an indirect (direct) band gap semiconductor for the spin-up (spin-down) branch. This suggests that the CeOCl can be expected to be a semiconductor material. In addition, <i>in</i> <i>situ</i> high-pressure angle-dispersive X-ray diffraction experiment reveals that the bulk modulus of CeOCl is 52.8(8) GPa, which is close to our first-principles calculations, giving that <i>B</i><sub>0</sub> = 47.6(5) GPa
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